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Revision difference : meager
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A meager or Baire \emph{first category} set in a topological space is one which is a countable union of nowhere dense sets. A Baire \emph{second category} set is one which contains a countable union of open and dense sets. A meager or Baire first category set in a topological space is one which is a countable union of nowhere dense sets. A Baire second category set is one which contains a countable union of open and dense sets.